1. Field of the Invention
The invention relates to data storage technology, and in particular, to a data storage device utilizing storage media with a liquid lubricant interface between the storage media and the data recording head.
2. Description of the Related Art
The data storage industry has followed a continuing trend of decreasing the physical size of storage components, while maintaining or increasing the quantity of data stored by the component. In the field of data storage on magnetic disks, or "disk drives," reductions in physical size have followed a trend of reducing the physical space occupied by the storage device, or "form factor", by approximately one-half. Thus, the length of a succeeding series of drives has equaled the width of the previous series of drives, and the width of the succeeding drive equalled approximately one-half the length of the preceding drive series. The physical height of the drives has followed a less orderly progression, beginning first with the "full height" drives, approximately 3.3" high, sized to fit into a drive bay of an IBM personal computer, then the 1.62" "half-height" drives, followed by even shorter 1" and 3/4" height drives.
Disclosed in co-pending application Ser. No. 07/508,960, is a disk drive having a two and one-half inch (21/2") form factor in which the length of the drive is approximately the width of a three and one-half inch (31/2") drive and the width is approximately one-half of the length of a 31/2" drive. The dimensions of the disk drive are: length 4 inches, width 23/4 inches, and height approximately 0.68 inch. One embodiment of the disk drive weights less than approximately six (6) ounces, and the single disk in the drive has a diameter of approximately 2.56 inches.
The overall power consumption of the disk drive is less than 3.5 watts and the power consumption may be as low as 1.5 watts during idle periods. Thus, the disk drive is ideal for use in portable or other battery powered computers. The power consumption of the disk drive is further reduced by the use of a sleep mode to less than 0.5 watt. A closed loop, embedded servo control system provides the single two and one-half inch diameter disk with a storage capacity of 20 Mb.
The drive disclosed in the '960 application incorporates an air bearing read/write head positioned over the surface of the magnetic recording disk to read data from and record data on the disk surface. Although continual contact between the transducer (typically a read/write head mounted on a slider) and the magnetic storage medium is advantageous from a magnetic perspective, such arrangement is undesirable because wear and material interactions lead to degraded system reliability and performance. Accordingly, one paramount consideration in designing magnetic recording systems is the maintenance of spacing between the head and medium.
Conventionally, air bearing sliders have been limited to a flying height on the order of 2-3 .mu.inches. U.S. Pat. No. 5,097,368, owned by the assignee of the instant application, discloses an information recording apparatus with a non-newtonian liquid bearing between the head and the disk which allows the head to achieve a lower interface distance between the head and the disk than generally possible with air bearing slider configurations. A major problem in the practical implementation of disk drives incorporating a liquid lubricant at the head-disk interface is the maintenance of the liquid bearing on the surface of the disk in no matter what orientation the drive may encounter during operation; that is, the liquid lubricant must be maintained on the disk in whatever attitude the drive takes with respect to the force of gravity. Obviously, the force of gravity will induce the liquid to move to the lowest point in the drive at any given time. This problem may be viewed in two contexts: where the lubricant must be applied to the surface of the disk at a location and in a manner where the surface tension of the liquid bearing is sufficient to maintain a sufficient quantity of the liquid bearing at the head disk interface; and where constant circulation of the liquid bearing to the disk surface is assured, whatever orientation the disk drive takes with respect to gravity.
In European Patent No. 0367,510, a wick structure is shown for use in applying the liquid lubricant from a reservoir at a low point in the head disk enclosure to the surface at the inner diameter of the disk surface by capillary action. Various methods are also shown therein for recirculating the liquid bearing fluid to the wick structure. However, no mention is made of the problems associated with providing the liquid onto the disk surface at the various attitudes which a disk drive may encounter.
The orientation problem is particularly acute in notebook and laptop computers wherein the possible operating attitudes which the drive may encounter are likely to be numerous and varied.
A further problem with using a liquid bearing in a hard disk drive involves preventing leakage of the liquid bearing from the drive. The non-Newtonian fluids which are most advantageously used as liquid bearings in such drives have low viscosity, and conventional sealing techniques used for disk drives are only partially effective in preventing leakage of the liquid bearing from the drive. Leakage must be prevented since only a finite amount of lubricant will be included in the drive prior to provision to end users. In addition, leakage would result in problems of contamination or damage to the host system.
An additional problem in using a liquid bearing in drives concerns the compatibility of such non-Newtonian fluids with conventional materials utilized in manufacturing parts for the drives. In particular, ball-bearing grease conventionally used as actuator and spin motor ball-bearing lubricants, adhesives used to secure bearings and other drive components, and plastics used in headers and flex circuits, all used in air bearing disk drives, are susceptible to the solvent characteristics of the non-Newtonian fluids. As a result, such materials can decompose and cause contamination within the controlled, internal drive environment.
In addition, the properties of such non-Newtonian fluids are susceptible to temperature changes. In particular, the vapor pressure and viscosity of the liquids change to varying degree with increases or decreases in temperature. Thus, such effects must be accounted for in providing a lubricated disk drive suitable for use in a laptop or notebook computer.
Finally, drag is a significant problem in a lubricated disk drive. In particular, movement of the read/write head over a fluid, even a non-Newtonian fluid, causes drag on the head and, where used, an applicator wick. Such drag is not present in an air bearing disk drive since air has very low viscosity. This drag must be accounted for in both terms of reducing the total drag on the head through a head design which provides the least amount of drag possible, and in terms of ensuring that the actuator and spindle motor can accommodate any drag which cannot be reduced through the head design. In addition, the liquid bearing applicator must be designed to achieve low drag.
The present invention is directed to a two and one-half inch diameter disk drive with enhanced storage capacity provided by allowing the head disk interface distance to be reduced to a flying height of two .mu.inches or less.